Nov. 1845.] Rotation of a Ray of Light by Electric Force. 305 



ratus may be stated as follows: — The tube within the long helix 

 (2190.) was filled with distilled water and placed in the line 

 of the polarized ray, so that by examination through the eye- 

 piece (2150.), the image of the lamp-flame produced by the 

 ray could be seen through it. Then the eye-piece was turned 

 until the image of the flame disappeared, and, afterwards, the 

 current often pairs of plates sent through the helix; instantly 

 the image of the flame reappeared, and continued as long as 

 the electric current was passing through the helix ; on stop- 

 ping the current the image disappeared. The light did not 

 rise up gradually, as in the case of electro- magnets (2170.), 

 but instantly. These results could be produced at pleasure. 

 In this experiment we may, I think, justly say that a ray of 

 light is electrified and the electric forces illuminated. 



2196. The phaenomena may be made more striking, by the 

 adjustment of a lens of long focus between the tube and the 

 polarizing mirror, or one of short focus between the tube and 

 the eye; and where the helix, or the battery, or the substance 

 experimented with, is feeble in power, such means offer assist- 

 ance in working out the effects : but, after a little experience, 

 they are easily dispensed with, and are only useful as accesso- 

 ries in doubtful cases. 



2197- In cases where the effect is feeble, it is more easily 

 perceived if the Nichol eye-piece be adjusted, not to the per- 

 fect extinction of the ray, but a little short of or beyond that 

 position ; so that the image of the flame may be but just visible. 

 Then, on the exertion of the power of the electric current, the 

 light is either increased in intensity, or else diminished, or 

 extinguished, or even re-illuminated on the other side of the 

 dark condition ; and this change is more easily perceived than 

 if the eye began to observe from a state of utter darkness. 

 Such a mode of observing also assists in demonstrating the 

 rotatory character of the action on light; for, if the light be 

 made visible beforehand by the motion of the eye-piece in one 

 direction, and the power of the current be to increase that 

 light, an instant only suffices, after stopping the current, to 

 move the eye-piece in the other direction until the light is ap- 

 parent as at first, and then the power of the current will be to 

 diminish it; the tints of the lights being affected also at the 

 same time. 



2198. When the current was sent round the helix in one 

 direction, the rotation induced upon the ray of light was one 

 way ; and when the current was changed to the contrary di- 

 rection, the rotation was the other way. In order to express 

 the direction, I will assume, as is usually done, that the cur- 

 Phil. Mag. S. 3. Vol. 28. No. 1 87. April 1846. Y 



